Over 50% of Americans are regular coffee drinkers, consuming an estimated 400 million cups daily. Coffee has been perking up lives for centuries. But little has been known about the daily grind’s health benefits. Some studies claim that coffee has harmful side effects. But it has not affected Americans’ appetites for the drink.

Positive news has been brewing about coffee’s potential benefits, with some caveats, of course. Two recent studies link moderate to heavy coffee drinking with specific health benefits. In an analysis published in the Archives of Internal Medicine, people who drink 3-4 cups of Joe a day were one-fourth less likely to develop type 2 diabetes than those who drank fewer than two cups. And men drinking at least six cups a day had a 60% lower risk of developing an aggressive form of prostate cancer than those who were java teetotalers.

What about an overall effect of coffee on mortality rates? There have been conflicting studies over the years. However, in 2008, reduced mortality rates from coffee consumption were found in a study published in the Annals of Internal Medicine. Researchers from Harvard University and the University of Madrid analyzed data from more than 84,000 women who participated in Harvard’s Nurse’s Health Study and more than 41,000 men who participated in a companion study involving male health professionals.

None of the participants in either study had cancer or heart disease at enrollment, and all completed diet and health questionnaires every 2-4 years that included questions about coffee consumption. The nurses were followed for 24 years and the men for 18 years. After controlling for risk factors such as diet, weight, smoking status, and disease status, researchers concluded that those who drank coffee were less likely to die than those who did not. It was felt that the risk reduction was primarily attributable to a lower risk of death from heart disease while a significant affect on cancer mortality wasn’t observed.

Earlier studies have linked coffee consumption with a reduction in a variety of cancers such as colon, mouth, throat, esophagus, and endometrial. The Harvard study didn’t observe cancer reductions. Other studies have found that coffee drinkers are also less likely to have cavities, gallstones, cirrhosis of the liver, Parkinson’s disease, Alzheimer’s disease, or commit suicide.

But coffee isn’t for everyone. It contains potent chemicals that seem to adversely affect some persons more than others.

Caffeine has powerful, systemic effects on many organ systems, including the brain and cardiovascular system. It’s chemically related to certain ingredients in chocolate, which also contains small amounts of actual caffeine. Caffeine has been known to raise blood pressure, heart rate and levels of homocysteine, an amino acid linked to increased rates of stroke and heart disease. Higher rates of miscarriage and low birth-weight babies have been associated with pregnant women who drink two or more cups of coffee a day. Caffeine has also been implicated in bone loss in elderly women and benign breast lumps.

Some people seem quite sensitive to the stimulant effects of the brew. Coffee has been known to exacerbate anxiety, irritability, heartburn, and insomnia. For those who’ve developed caffeine tolerance, withdrawal can include headache, nausea, stomach pains, irritability and drowsiness. The onset of withdrawal typically occurs with 24 hours and may last for five days. Moderate amounts of caffeine may be the best way to take the edge off withdrawal symptoms.

For pregnant women and those with osteoporosis, high blood pressure, diabetes, anxiety disorders, and insomnia, drinking coffee may lead to undesirable side effects. Be sure to consult with your physician about the relative risks of coffee drinking.

For the rest of us, coffee in moderation is probably the best guide for now. This daily habit will probably cause little harm and may have some longer-term health benefits.